Thermal and irradiation resistance of folic acid encapsulated in zein ultrafine fibers or nanocapsules produced by electrospinning and electrospraying.

The objectives of this study were to characterize zein fibers and capsules prepared by electrospinning and electrospraying techniques, respectively, and then use them to encapsulate folic acid. Folic acid containing fibers and capsules (0.5, 1.0, and 1.5%, w/v) were submitted to thermal treatment (100, 140, and 180 °C) and ultraviolet A light (UVA) irradiation to evaluate the resistance of folic acid. Zein fibers and capsules containing folic acid showed high encapsulation efficiency (>80%). Unencapsulated folic acid showed a reduction in folic acid content from 17.17 µg/mL to 5.44 µg/mL (approximately 70%) when exposed to 180 °C. Photodegradation of unencapsulated folic acid lowered its concentration from 17.17 µg/mL to 12.58 µg/mL (~26% of reduction), when exposed for 1 h to UVA irradiation. However, folic acid concentration when encapsulated in fibers (1.5%) was maintained or only slightly reduced from 9.73 µg/mg to 8.88 µg/mg after thermal treatment at 180 °C. The capsules containing 1.5% of folic acid also presented a slight reduction in folic acid concentration from 8.84 µg/mg to 7.88 µg/mg when exposed to 24 h of UVA irradiation. Zein fibers and capsules containing folic acid present promising characteristics for application in foods that require thermal processing or exposure to irradiation.

Phosphorylated Zein as Biodegradable and Aqueous Nanocarriers for Pesticides with Sustained-Release and anti-UV Properties.

Zein's prevalent hydrophobic character is one of the major challenges associated with ineffective utilization as an aqueous nanocarrier for pesticides. Herein, we report an effective approach to hydrophilic modification of zein by phosphorylation using nontoxic sodium tripolyphosphate (STP), thereby improving the water-solubility, foliage wettability, and adhesion ability of zein as a nanocarrier for sustained release of pesticides. The procedure relied on zein grafted with STP via N- and O- phosphate bonds and encapsulation of avermectin (AVM) as a hydrophobic model drug using phosphorylated zein (P-Zein), which achieved pH sensitivity to controlled release of AVM in various applicable environments. The chemical interaction between zein and STP was confirmed by Fourier transform infrared, thermogravimetric analysis, and differential scanning calorimetric. Scanning electron microscopy, dynamic light scattering, and zeta potential technique were applied to investigate their structural characteristics and stability, from which it was found that AVM encapsulated in P-Zein (AVM@P-Zein) formed uniform nanoparticles with average sizes in the range of 174-278 nm under different conditions, and had an excellent stability in aqueous solution. Besides, AVM@P-Zein facilitated the wettability on the foliage surface evidenced from contact angle values owing to the amphiphilic character after phosphorylation as well as enhanced the adhesion ability between liquid and leaf, restricting the pesticide runoff. Ultraviolet-visible spectroscopy was employed to explore the anti-UV property and encapsulation as well as release behavior, which revealed that the presence of P-Zein like a shell protects AVM from UV photolysis with encapsulation efficiency of approximately 81.52%, and the release of AVM from P-Zein showed pH-responsive behavior ascribed to protonation and deprotonation of phosphate under various pH conditions fitting to Elovich kinetic model, achieving the relatively more rapid release under acidic conditions. More importantly, AVM@P-Zein retained the toxicity for insecticidal effect.

Development and characterization of novel antimicrobial bilayer films based on Polylactic acid (PLA)/Pickering emulsions.

Biodegradable food packaging is sustainable and has a great application prospect. PLA is a promising alternative for petroleum-derived polymers. However, PLA packaging suffers from poor barrier properties compared with petroleum-derived ones. To address this issue, we designed bilayer films based on PLA and Pickering emulsions. The formed bilayer films were compact and uniform and double layers were combined firmly. This strategy enhanced mechanical resistance, ductility and moisture barrier of Pickering emulsion films, and concomitantly enhanced the oxygen barrier for PLA films. Thymol loadings in Pickering emulsion layer endowed them with antimicrobial and antioxidant activity. The release profile of thymol was well fitted with Fick's second law. The antimicrobial activity of the films depended on film types, and Pickering emulsion layer presented larger inhibition zone than PLA layer, hinting that the films possessed directional releasing role. This study opens a promising route to fabricate bilayer architecture creating synergism of each layer.

Biodegradable zein-based films: influence of gamma-irradiation on structural and functional properties.

Zein, a predominant corn protein, is an alcohol-soluble protein extracted from corn and is characterized by unique film-forming properties. The characteristic brittleness of zein diminishes its usefulness as a structural material. The objective of this work was to study the effect of gamma-irradiation on improving the performance of zein films in packaging applications. This goal has been achieved by irradiating zein film-forming solutions with various doses of gamma-rays, namely, 10, 20, 30, and 40 kGy at dose rate of 10.5 kGy/h, using a Co(60) gamma-radiation source. The impact of radiation process on the structural properties has been explored through far-UV CD spectral analysis and scanning electron microscopy. Additionally, viscosity changes that reflect the effect of radiation treatment on degradation and/or cross-linking of protein chains have been measured. However, improvements in the performance of zein films as packaging materials that can be accomplished by radiation treatment have been investigated via monitoring of the color, surface density, roughness, mechanical properties (tensile strength and elongation percentage), water uptake, and water barrier properties. The results indicated that gamma-irradiation treatment of the film-forming solution can be used to improve the water barrier properties, as well as color and appearance of the zein films. Moreover, a sterilization effect is considered to be an additional advantage for applying gamma- irradiation.

Complexation between dodecyl sulfate surfactant and zein protein in solution.

Interactions between sodium dodecyl sulfate and zein protein, a model system for the understanding of the effect of surfactants on skin, were investigated using a range of techniques involving UV-vis spectroscopy, TOC (total organic carbon analysis), electrophoresis, and static and dynamic light scattering. Zein protein was solubilized by SDS. The adsorption of SDS onto insoluble protein fraction caused the zeta potential of the complex to become more negative. From these values, we calculated the Gibbs energy of absorption, which decreases when the SDS concentration is raised. Finally the structure of the complex, based on the analysis by static and dynamic light scattering, is proposed to be rod like.